In an optical fiber communication system, the transceiver optical sub-assembly is an important medium for conversion between optical signals and electrical signals. There are different types of transceiver optical sub-assemblies, including a transmitter optical sub-assembly (TOSA) for transmitting optical signals, a bidirectional optical sub-assembly (BOSA) for bidirectional transmission of optical signals over one single optical fiber, and a tri-directional optical sub-assembly (TRI-DI OSA) for simultaneously receiving a digital signal and an analog signal and transmitting a digital signal. In FIG. 1, there is illustrated a BOSA. The BOSA includes a receptacle body 10, to which a light-emitting unit 11 and a light guide structure 12 are connected. The light-emitting unit 11 is located on a central axis of the receptacle body 10. The light-emitting unit 11 and the light guide structure 12 are optically aligned and coupled in precision. The light guide structure 12 can be divided into two types, namely, a pigtail type and a receptacle type. In FIG. 1, there is illustrated a pigtail type light guide structure.
In the receptacle body 10, there is installed a filter 13. The optical signal emitted from the light-emitting unit 11 is refracted by the filter 13 to change its incident direction, as indicated by the arrows A1, A2 in FIG. 1, so that the focusing position of the optical signal is also changed. Therefore, the light guide structure 12 must be shifted in x-axis, y-axis and z-axis directions for optical collimation, so that the optical signal A2 of the light-emitting unit 11 and an optical fiber 14 held in the light guide structure 12 can be optically coupled and aligned with each other. Then, the light guide structure 12 is fixedly connected to the receptacle body 10 using a laser welding apparatus. However, when the laser welding is completed, the light guide structure 12 tends to warp due to thermal expansion. As a result, the light guide structure 12 is prevented from being fully connected to the receptacle body 10 and a gap S is formed between the light guide structure 12 and the receptacle body 10. This condition will cause optical power shift to result in optical power loss.